Bi-rate high definition television signal transmission system

Abstract

A frame of compressed video data is formatted for transmission into a plurality of data segments, a first group of which are encoded in the form of a plurality of four-level symbols and a second group of which are encoded in the form of a plurality of two-level symbols for providing improved noise performance. The partition between the first and second groups of data segments may be established on a fixed basis, a variable basis dependent upon the effective level of compression, or a combination of both. Preferably, the levels are selected such that the average levels of the transmitted M and N-level symbols are substantially equal to a non-zero value to assist lock-up of the receiver PLL and reduce transmission power.

I claim: 
     
       1. A system for transmitting a video data signal comprising: means for variably compressing said video data signal;   means for formatting said compressed signal into a plurality of data frames, each including a plurality of data segments;   means for encoding a first group of the data segments of each of said frames in the form of a plurality of N-level symbols characterized by a constant symbol rate and for encoding the remaining data segments of each respective frame in the form of a plurality of M-level symbols characterized by said constant symbol rate, where M is greater than N, whereby each of said M-level symbols represents a greater number of data bits than each of said N-level symbols, said first group of data segments including a control signal identifying the data segments comprising said first group of data segments and the data segments comprising said remaining data segments; and   means for transmitting said M and N-level symbols.   
     
     
       2. The system of claim 1 including buffer means coupled between and controlling the operation of both said compressing and encoding means as a function of the fullness thereof. 
     
     
       3. The system of claim 1 wherein said M and said N levels are selected such that the average levels of said transmitted M and N-level symbols are substantially equal. 
     
     
       4. The system of claim 3 wherein said average levels are a non-zero value. 
     
     
       5. The system of claim 1 wherein the levels of said N-level symbols are intermediate adjacent levels of said M-level symbols. 
     
     
       6. The system of claim 5 wherein M=4 and N=2. 
     
     
       7. The system of claim 6 wherein the normalized values of the levels of said M-level symbols are -2, 0, +2 and +4, and of said N-level symbols are -1 and +3. 
     
     
       8. The system of claim 1 wherein the levels of said N-level symbols comprise a subset of the levels of said M-level symbols. 
     
     
       9. The system of claim 2 including means for ordering the compressed video data according to its relative importance and control means responsive to the fullness of said buffer means for variably partitioning said ordered data into a first portion comprising the more important compressed video data which is encoded in the form of said N-level symbols and a second portion comprising the less important video data which is encoded in the form of said M-level symbols. 
     
     
       10. The system of claim 1 wherein said control signal comprises a signal identifying the number of data segments comprising said first group of data segments. 
     
     
       11. A television signal transmission system comprising: means for compressing said television signal;   means for formatting said compressed signal into a plurality of data frames, each including a plurality of data segments;   means for encoding a first group of the data segments of each of said frames in the form of a plurality of N-level symbols characterized by a constant symbol rate and for encoding the remaining data segments of the respective frame in the form of a plurality of M-level symbols characterized by said constant symbol rate, where M is greater than N, whereby each of said M-level symbols represents a greater number of data bits than each of said N-level symbols, said first group of encoded data segments including a control signal identifying the data segments comprising said first group of data segments and the data segments comprising said remaining data segments, and where the average levels of said N-level symbols and said M-level symbols are substantially equal to the same non-zero value;   means for transmitting said encoded data segments over a selected channel; and   means for receiving said transmitted data segments and reconstructing therefrom a fixed rate output signal representing said television signal.   
     
     
       12. The system of claim 11 wherein said first group of data segments represents a variable portion of each respective data frame which includes a fixed number of data segments in which said control signal is encoded as a plurality of said N-level symbols. 
     
     
       13. The system of claim 11 including buffer means coupled between and controlling the operation of both said compressing and encoding means as a function of the fullness thereof. 
     
     
       14. The system of claim 11 wherein said control signal comprises a signal identifying the number of data segments comprising said first group of data segments. 
     
     
       15. A television signal receiver comprising: means for receiving a television signal comprising a plurality of data frames each including a plurality of data segments, each of said data frames comprising a first group of data segments comprising a plurality of N-level symbols characterized by a constant symbol rate and the remaining data segments of the respective frame comprising a plurality of M-level symbols characterized by said constant symbol rate, where M is greater than N, whereby each of said M-level symbols represents a greater number of data bits than each of said N-level symbols, said first group of data segments further including a plurality of N-level symbols representing a control signal identifying the data segments comprising said first group of data segments and the data segments comprising said remaining data segments; and   means responsive to said received television signal for providing a fixed rate binary output signal representing received television information.   
     
     
       16. The receiver of claim 15 wherein said M and said N levels are selected such that the average levels of said received M and N-level symbols are substantially equal. 
     
     
       17. The receiver of claim 16 wherein said average levels are a non-zero value. 
     
     
       18. The receiver of claim 15 wherein the levels of said N-level symbols are intermediate adjacent levels of said M-level symbols. 
     
     
       19. The receiver of claim 18 wherein M=4 and N=2. 
     
     
       20. The receiver of claim 19 wherein the normalized values of the levels of said M-level symbols are -2, 0, +2 and +4, and of said N-level symbols are -1 and +3. 
     
     
       21. The receiver of claim 15 wherein the levels of said N-level symbols comprise a subset of the levels of said M-level symbols. 
     
     
       22. The receiver of claim 15 wherein said first group of data segments represents a variable portion of each respective data frame which includes a fixed number of data segments in which said control signal is encoded, said receiver including means responsive to said received control signal for decoding said receiving N-level and M-level symbols. 
     
     
       23. The receiver of claim 15 wherein said control signal comprises a signal identifying the number of data segments comprising said first group of data segments. 
     
     
       24. A television signal receiver comprising: means for receiving a video signal comprising a plurality of data frames each including a plurality of data segments, each of said data frames comprising a first group of data segments including a plurality of N-level symbols characterized by a predetermined symbol rate and the remaining data segments of each respective data frame comprising a plurality of M-level symbols characterized by said predetermined symbol rate, where M is greater than N and where the average levels of said N and M-level symbols are substantially equal to the same non-zero value, whereby each of said M-level symbols represents a greater number of data bits than each of said N-level symbols, said first group of data segments further including a plurality of N-level symbols comprising a control signal identifying the data segments comprising said first group of data segments and the data segments comprising said remaining data segments; and   means responsive to said control signal for decoding said first and second plurality of symbols for providing a fixed rate binary output signal representing a received video image.   
     
     
       25. The receiver of claim 24 wherein the levels of said N-level symbols are intermediate adjacent levels of said M-level symbols. 
     
     
       26. The receiver of claim 25 wherein M=4 and N=2. 
     
     
       27. The receiver of claim 26 wherein the normalized values of the levels of said M-level symbols are -2, 0, +2 and +4, and of said N-level symbols are -1 and +3. 
     
     
       28. The receiver of claim 24 wherein said first group of data segments represents a variable portion of each respective data frame in which said control signal is encoded. 
     
     
       29. The receiver of claim 24 wherein said control signal comprises a signal identifying the number of data segments comprising said first group of data segments. 
     
     
       30. A method of transmitting a television signal comprising: formatting said television signal into a plurality of data frames, each including a plurality of data segments;   encoding a first group of said data segments of each of said frames in the form of a plurality of N-level symbols characterized by a constant symbol rate and encoding the remaining data segments of each respective data frame in the form of a plurality of M-level symbols characterized by said constant symbol rate, where M is greater than N, whereby each of said M-level symbols represents a greater number of data bits than each of said N-level symbols, said first group of data segments including a plurality of N-level symbols representing a control signal identifying the data segments comprising said first group of data segments and the data segments comprising said remaining data segments; and   transmitting said data segments over a selected channel.   
     
     
       31. The method of claim 30, wherein said first group of data segments comprises a variable portion of the respective data frame. 
     
     
       32. The method of claim 31 wherein said first group of data segments comprises a fixed number of data segments including said control signal. 
     
     
       33. The method of claim 30 wherein said M and said N levels are selected such that the average levels of said transmitted M and N-level symbols are substantially equal. 
     
     
       34. The method of claim 33 wherein said average levels are a non-zero value. 
     
     
       35. The method of claim 30 wherein the levels of said N-level symbols are intermediate adjacent levels of said M-level symbols. 
     
     
       36. The method of claim 35 wherein M=4, N=2 and the normalized values of said M-level symbols are -2, 0, +2 and +4 and of said N-level symbols are -1 and +3. 
     
     
       37. The method of claim 30 wherein the levels of said N-level symbols comprise a subset of the levels of said M-level symbols. 
     
     
       38. The method of claim 30 including both compressing said television signal and establishing the number of data segments comprising said first group as a function of a common criteria. 
     
     
       39. The method of claim 30 including receiving and decoding said transmitted N and M-level symbols for providing a fixed rate output signal. 
     
     
       40. The method of claim 30 including receiving said transmitted N and M-level symbols and decoding the received symbols in response to said control signal for providing a fixed rate binary output signal. 
     
     
       41. The method of claim 30 wherein said control signal comprises a signal identifying the number of data segments comprising said first group of data segments. 
     
     
       42. A system for transmitting a video signal comprising: means for deriving a compressed video signal having components of higher and lesser importance for image reproduction;   means for encoding the components of said video signal of higher importance as a first series of data segments and for encoding the components of lesser importance as a second series of data segments, the encoded first series of data segments having a greater level of noise immunity and a lower bit-rate than the encoded second series of data segments, said first series of data segments including a fixed number of data segments comprising a control signal identifying the data segments comprising said first and second series of data segments; and   means for transmitting said first and second series of data segments.   
     
     
       43. The system of claim 42 including means for receiving said transmitted first and second series of data segments and means responsive to said received control signal for decoding the components encoded in said data segments. 
     
     
       44. The system of claim 42 including a buffer for receiving said compressed video signal, said first and second series of data segments being established in response to the fullness of said buffer. 
     
     
       45. A television signal receiver comprising: means for receiving a compressed video signal comprising a first plurality of encoded video components forming a first series of data segments and a second plurality of encoded video components forming a second series of data segments, said first series of data segments including a control signal identifying said first and second series of data segments, the encoded components of said first series of data segments having a greater level of noise immunity and a lower bit-rate than the encoded components of said second series of data segments; and   means responsive to said received control signal for decoding said first and second pluralities of received video components.